You are talking about people here that rely quite heavily on other peoples work, and since a certain retro thing seems to make the rounds yet again, it is hardly surprising that things are coming back.
I'd be interested to see someone , using the tools and devices and elements from the things you mention and really do something worthwhile and interesting with them( If you know anyone, I'd love to check them out!).
Just sampling stuff as happens a lot these days is quite pathetic I think
I think all four are quite irrelevant and won't be heard off in a couple years time...unless they have a psycho fit, kiss madonna on TV , strip off or go out looking like they are on the way to a fancy dress party, or have a public break up after ten minutes of marriage, or maybe get a spot on something like x-factor or any one of the millions of 'talent shows'.( I am not saying that they are not good/decent/passable/lucky singers, by the way!

)